What minimum frequency of light is required to ionize potassium?

NetherCraft 0

The energy required to ionize potassium is 419 kj/mol

What minimum frequency of light is required to ionize potassium?

____ s^-1

please help, thanks

2 Answers

  • We find the work function per atom e = E/N = 419000/6.023E23 = hf = photon energy; solve for the frequency, using N = 6.023E23 atoms per mole and Planck’s h = 6.63E-34 J.s:

    f = E/Nh = 419000/(6.023E23*6.63E-34) = 1.04927E+15 = 1.05E15 cps. ANS.

  • Ionization energy = 419kJ/mol = 419000J/mol (since 1kJ = 100J)

                          = 419000/ 6.023*10^23 J/atom (since 1 mol = 6.023*10^23molecules)
    
                          = 69.56*10^-20 J/molecule

    Energy of a photon = hn (where n is the frequency). Equating the two,

    6.65610^-34n = 69.56*10^-20

    => n = 1.0.45*10^15 s^-1

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